This invention is related to ionic complexes of iodine with chitosan or its derivatives, methods of preparation thereof and pharmaceutically useful compositions containing these complexes. This invention is also related to hydrogels made of chitosan-iodine ionic complexes. This invention further relates to methods of treatments by these preparations, and their use in promoting wound healing and as antiseptics.
Wounds are internal or external bodily injuries or lesions caused by physical, chemical, microbial, or thermal means. Natural wound healing involves a series of three processes:
a. An inflammation phase where platelet aggregation and clotting occur to stop bleeding and induce influx of various types of cells to start a cellular proliferation process;
b. A cellular proliferation phase where new connective or granulation tissue is formed; and
c. A remodeling phase where the granulation tissue is replaced by collagen and elastin fibers forming a scar.
The primary step in wound treatment is to prevent or eliminate microbial contamination of wounds by using disinfectants or antiseptics. Since contaminating microbes release toxins and cause pathological changes at the wound site, delaying the natural healing process, the use of antimicrobials is an essential first step in wound treatment.
Among antimicrobials, iodine in its elementary state exhibits a universal germicide activity against bacteria, fungi, and viruses and for this reason has been used in alcoholic solutions for decades. However, the limits to this use are the low stability of iodine solutions, its notable aggressiveness on tissues when applied as a solution, and the persistent staining it leaves on applied tissues.
More recently, water soluble forms of iodine (known as iodophors) have been commercialized which only partially reduced these undesirable side effects. The most common employed iodophor is polyvinylpyrrolidone-iodine, (also known as povidone iodine). Povidone iodine is used for pre-operative skin disinfections, wound disinfections, and as a mouthwash and vaginal antiseptic. However, in wound treatment, povidone iodine does not effectively promote good wound healing. In fact, it either impaired wound healing or reduced wound strength. (Kramer, J. Vasc. Nurs. 1999 March: 17(1) 17-23). In addition, povidone iodine showed negative effects on wound healing, similar to those of steroids (Kashyap et al., Am. Surg. 1995 June; 61(6) 486-491).
A few attempts to prepare iodine-containing compositions to mitigate the adverse effects of both elemental iodine and povidone iodine were made, using chitosan and its derivatives. Chitosan derivatives include, but are not limited to chitin, N-carboxybutylchitosan, N-acylchitosan, N-carboxymethylchitosan, N-O-carboxymethylchitosan and N-O-chitosan sulphate. (See U.S. Pat. Nos.: 4,275,194 and 5,538,955).
Chitosan is a cationic polysaccharide obtained by deacetylation of the natural polymer chitin. Kato et al. (U.S. Pat. No. 4,275,194) have described a process to prepare chitosan iodine adducts for a disinfectant and a deodorant use. The process involved many days of impregnation and drying and the final product was recovered in the form of dry dark brown powder. The mentioned method failed to provide a commercially feasible way for production and use, due to the extensive time periods required for preparation and the inconvenient non-liquid form of the product.
Because chitosan and derivatives have been recognized for their wound healing activity, DeRosa et al. (U.S. Pat. No. 5,538,955) have described different procedures to prepare solid forms of chitosan-iodine products. Those procedures required the use of elevated temperatures, special reactors for hazardous iodine gas, and took up to 5 days to complete. The resultant solid product took one to two days to dissolve in a suitable liquid. DeRosa et al. also suggested a liquid chitosan iodine preparation using high concentrations of surfactants. Because surfactants are known for their ability to dissolve or modify natural cell lipid membranes, they can damage the protective barrier nature of the skin, causing skin tissue destruction and delayed wound healing.
Despite the fact that chitosan iodine products have been proposed for more than twenty years, a clinically and pharmaceutically acceptable liquid formulation is yet to be established. It is the purpose of this invention to disclose a practical, fast and efficient method of preparing chitosan iodine liquid preparations that will eliminate the above mentioned limitations of iodine, povidone iodine and previously disclosed chitosan iodine compositions.
This invention also has superior utility in promoting wound healing without the need of additional medications such as growth factors (Drohan et al, U.S. Pat. No. 6,124,273) or immobilized heparin (Kratz et al., Scand. J. Plast. Reconstr. Surg. Hand Surg. 1997). In the prior art formulations, such medications or supplements were required to overcome the limited efficiency of chitosan when used as a sole wound healing promoter.
It is the object of this invention to provide liquid chitosan iodine compositions suitable for treatment of wounds by acting as antiseptics and a wound healing promoters. Another object of this invention is the formation of said useful compositions as ionic complexes between positively charged chitosan molecules in solution and the solution of the small anionic iodine-iodide complexes (will be referred to as ionic chitosan iodine complex or ICIC""s). A further object of this invention is the preparation of said compositions without the need of heat, special reactors, surfactants or volatile solvents, such as alcohol. A further object of this invention is a composition of ICIC""s formulated as a hydrogel and the use thereof to promote wound healing.
In accordance with the present invention, it has been discovered that, unlike previously disclosed iodine based compositions, identified as adducts or charge transfer complexes, ICIC""s were found to possess dramatically higher viscosity and instantly form a gel structure that easily disperses upon shaking. A further discovery is that the color of ICIC""s is dark purple which is easily distinguished from the dark brown or orange yellow colors of other chitosan iodine complexes. A yet further advantage of this invention is that treatment with the compositions of the invention results in fast wound healing, minimal scar formation. Furthermore, permanent staining of the skin does not occur.
In one embodiment, this invention provides a composition of matter comprising an ionic complex between cationic chitosan molecules in solution and a monovalent, anionic small complex made of iodine-iodide (I3xe2x88x92). A second embodiment of this invention involves the existence of ICIC in a hydrogel form suitable for direct application to intact or wounded skins of animals or humans. A third embodiment of this invention involves the formation of such complex in a homogeneous hydrogel form, without the need of any additional polymers or thickening agent. A fourth embodiment of this invention involves casting ICIC hydrogel into solid powder or flexible films or otherwise suitable films or sheets or the like.
The pharmaceutical compositions of this invention include, without limitation:
1. Chitosan, or derivative, having an average molecular weight between 10 to 1000 kilo Daltons, preferably in the range of 100-800 kilo Daltons, and most preferably in the range of 250 to 750 kilo Daltons. The degree of deacetylation of chitosan is 40% to 95%, preferably 60% to 90%.
2. An aqueous vehicle that may include:
a. An acid from the group of acetic, lactic, citric, glycolic, and the like, or their buffers or salts, at a concentration resulting in pH values of the final composition between 3.0 and 8.0, more preferably between 4.0 and 7.0.
b. A low molecular-weight diol, such as ethylene or propylene glycol, a triol such as glycerol, or a polyol such as sorbitol or polyethylene glycol, at a concentration range between 5% and 25%.
3. Elemental iodine at the concentration range of 0.05% to 5.0%, preferably at the concentration range of 0.1% to 1%.
4. An iodide source such as potassium iodide, sodium iodide, or zinc iodide or the like, at a concentration range of 0.05% to 5%, preferably at a concentration range of 0. 1% to 1.0%, or hydroiodic acid of similar concentrations.
In this invention, the low-molecular weight diol, triol, or polyol functions as a xe2x80x9cnon-volatilexe2x80x9d compound. As used herein, the expression xe2x80x9cnon-volatilexe2x80x9d means having a boiling point equal to or greater than the boiling point of ethylene glycol, that is, greater than or equal to 198xc2x0 C.
It has been discovered that the compounding order of the above composition is very critical and has to be performed so that both the cationic polymer and the iodine-iodide complex are prepared in separate portions of the aqueous vehicle prior to final mixing.
An advantageous feature of this invention is the instant formation of ICIC in a gel form following the mixing of the cationic and anionic components. The formed gel will provide utmost physical stability of the product during storage, yet can easily be transformed into pourable fluid upon gentle shaking. The pourable fluid form has the advantage of easily spreading on wounds or skin without the need of rubbing. Another advantage of this invention is that, once ICIC""s stay in contact with tissues, they transform back to a protective flexible film that will protect the wound from the surrounding environments, and slowly release active iodine for disinfecting the tissue.
The formed protective film can also control oxygen permeability to the wound and eliminate the need of using occlusive bandages. The formed film can also prevent the need for frequent wound treatments, which are usually painful. Another advantage of ICIC hydrogel is their ability to be cast and dried into flexible sheets or films that can serve as self-medicated bandages. Such bandage can absorb wound discharge, accelerating wound repair. A further advantage of these dried films is they can be naturally degraded by tissue enzymes without the need to remove them.
The following examples further illustrate the composition and use of this invention and are not intended to be limiting.